The present invention relates to a data communication apparatus which receives a radio wave transmitted from an antenna to generate power for communication.
Conventionally, a high frequency tag (RF. TAG), which generates power by a radio wave transmitted from an antenna and transmits information which has been stored therein, has been developed and used for a gate of the ski lift, gate at the station, sorting of parcels and the like.
The high frequency tag is provided with a non-volatile memory and a transmission/reception mechanism, but not with a power supply source such as a battery. In addition, power is generated by the received radio wave (a high frequency signal). Thus, the power supply source needs not be provided therein and information exchange can be performed for a long period of time. Further, remote (non-contact) data communication can advantageously be performed as it is performed by the radio wave.
For a system in which such communication apparatus (hereinafter referred to as xe2x80x9ca responderxe2x80x9d) is used, one type of radio wave (one-wave mode) or two types of radio waves (two-wave mode) may be transmitted from the other communication apparatus (hereinafter referred to as xe2x80x9can interrogatorxe2x80x9d). Only one type of carrier with information is transmitted from the responder in a one-wave mode, so that the carrier is rectified to generate power and also detected to obtain information.
On the other hand, for the responder in a two-wave mode, a first carrier for generation of power which has not been modulated and a second carrier with information are transmitted. Thus, the first and second carriers are separately received, so that the first carrier is rectified to generate power and the second carrier is detected to obtain information.
Since responders used in these modes (e.g., high frequency tags) are of course different in structure, the responder used in one mode cannot be used in the other mode. Therefore, two types of responders are required to perform communication in both modes. Accordingly, two types of integrated circuits (IC) forming the responders must be manufactured. This disadvantageously results not only in increase in the designing, manufacturing and product cost, but also in complicated management of the products (integrated circuit, communication apparatus and the like) for proper use.
An object of the present invention is to provide a data communication apparatus (a responder) which can be used both in one-wave and two-wave modes.
The object of the present invention is achieved by a data communication apparatus for data communication with an interrogator including: a power generating circuit generating power by a signal having a first frequency transmitted from the interrogator; and a modulating circuit modulating the signal having the first frequency in accordance with response information for an interrogation data when the signal having the first frequency transmitted from the interrogator has been modulated in accordance with the interrogation data, and modulating a signal having a second frequency in accordance with response information for an interrogation data obtained by demodulating the signal having the second frequency transmitted from the interrogator when the signal having the first frequency transmitted form the interrogator has not been modulated.
An advantage of the present invention is that one data communication apparatus (responder) enables communication both in the one-wave mode and two-wave mode, so that two types of data communication apparatuses are not necessary. In addition, since two types of integrated circuits forming the data communication apparatuses needs not be manufactured, reduction in the designing, manufacturing and product cost is achieved and management of the products (integrated circuits or communication apparatuses) for proper use is facilitated.